1. Field of the Invention
The present invention relates generally to systems and methods for enhancing the performance of sound reproduction and reinforcement systems and more particularly for enhancing the performance of these systems over broad listener areas.
2. Description of the Related Art
Since the advent of sound recording near the end of the nineteenth century, an effective methodology has been sought to make the reproduction of sound, especially music, approach as closely as possible the sound field created by the original live source. Challenges remain including increasing the audience listening area in which sound is faithfully reproduced. Sound reproduction system engineering implementations have focused on “electrostatic emitters” which are extremely directional in their radiation response and offer only a single listening location and electrodynamic emitters which have been designed for the uniform distribution of sound energy over a wide area.
Despite occasional announcements that the ultimate perfection has been reached and despite the increased number of separate emitters being utilized to create a theater or high-end home sound reproduction system, fidelity problems remain. Relatively accurate reproduction tends to exist. Unfortunately, it is restricted to central on axis listening positions, which are locations that are equidistant from primary emitters. For other listening positions spatial anomalies distort the associated sound field. With conventional approaches, for listening locations that are off the central axis of the emitters the “stereo image” degenerates. Consequently, for a group of original sound sources, such as instruments being played together, in a live performance the spatial orientation of the reproduced sound sources would not be the same as the spatial orientation of the live performance. Instead, the spatial orientation of the reproduction is compressed, expanded or otherwise changes relative to the spatial orientation of the original performance based upon listening position. In live performance sound reinforcement installations where emitters are used to reinforce the sound produced by instruments being played and singers' voices, performance frequently declines to the point where the emitters being used become the only acoustic image realized.
Since sound obeys an inverse square law relative to distance, as the distance between emitters and listener increases, the sound intensity decreases. As a result, the sound images that are created by two or more emitters at any listening position not equidistant from both emitters will have a geometry distortion introduced. In these off-axis listener positions, the instruments become crowded together and the instrument closest to the off axis listener becomes louder and the “stereo image” of central instruments rapidly degenerates. The incorporation of a third “center channel” has been tried, but this can add significantly to the system's complexity, and offers limited results.
A number of other devices have been proposed to increase the area in which the audience will experience faithful sound reproduction. Some have proposed the use of frequency sensitive elements to selectively phase shift and redirect the electrical energy to various emitter means. The proposed devices tend to add complexity and degrade the final reproduced sound. Others have proposed devices that attempt to stimulate the listening room utilizing radiation from the emitter without regard to room dependant anomalies such as wave cancellations that occur from reflective walls to produce an improvement.
Further, the industry has expended a great deal of effort measuring the effect of interaural time difference (ITD). This involves the time difference created by the physical path length difference created by the human head and the time differences created by the path lengths from sound source to listener. Various methods have been proposed to compensate for geometric anomalies. In modern recording studios it is common practice to use many microphones and recorder channels to capture a performance. Results can be disappointing since time and phase information that relate one instrument to another can be lost prior to recording distribution and is usually unavailable to sound reinforcement systems. As a result a less than ideal situation occurs in which differences in loudness of emitters are relied upon as the cues for spatial location to recreate sound image files. The challenge of increasing the audience listening area in which sound is faithfully reproduced remains by in large elusive.